In situ preparation of cubic Cu2O-RGO nanocomposites for enhanced visible-light degradation of methyl orange

Preparation and characterization of cellulose-chitosan/β-FeOOH composite hydrogels for adsorption and photocatalytic degradation of methyl orange

Biopolymer-based hydrogels have received great attention in wastewater treatment due to their excellent properties, e.g., high adsorption capacity, fast kinetics, reusability and ease of operation. In the present work, cellulose-chitosan/β-FeOOH composite hydrogels were prepared via co-dissolution and regeneration process as well as hydrothermal in situ synthesis of β-FeOOH. Effect of β-FeOOH loading on the properties of the composite hydrogels and the removal efficiency of methyl orange (MO) was investigated. Results showed that β-FeOOH was uniformly loaded onto the hydrogel framework, and the nanoporous structure of composite hydrogels could increase not only the effective contact area between β-FeOOH and the pollutants but also the active sites. Moreover, the increased β-FeOOH loading led to the enhanced MO removal rate under light conditions. When the loading time was extended from 6 h to 9 h, the MO removal rate increased by 21%, which can be mainly due to the photocatalytic degradation. In addition, MO removal rate reached 97.75% within 40 min under optimal conditions and attained 80.81% after five repetitions. The trapping experiment and EPR results indicated that the main active species were hydrogel radicals and holes. Consequently, this work provides an effective preparation approach for cellulose-chitosan/β-FeOOH composite hydrogel with high adsorption and photocatalytic degradation, which would hold great promise for wastewater treatment applications.

Cu2O/TiO2 decorated on cellulose nanofiber/reduced graphene hydrogel for enhanced photocatalytic activity and its antibacterial applications

Photocatalysis has gained attention as a viable wastewater remediation technique. However, the difficulty of recovering powder-based photocatalyst has often become a major limitation for their on-site practical application. Herein, we report on the successful in-situ preparation of a novel three-dimensional (3D) photocatalyst consisting of Cu₂O/TiO₂ loaded on a cellulose nanofiber (CNF)/reduced graphene hydrogel (rGH) via facile hydrothermal treatment and freeze-drying. The 3D macrostructure not only provides a template for the anchoring of Cu₂O and TiO₂ but also provides an efficient electron transport pathway for enhanced photocatalytic activity. The results showed that the Cu₂O and TiO₂ were uniformly loaded onto the aerogel framework resulting in the composites with large surface area with exposed actives sites. As compared to bare rGH, CNF/rGH, Cu₂O/CNF/rGH and TiO₂/CNF/rGH, the Cu₂O/TiO₂/CNF/rGH showed improved photocatalytic activity for methyl orange (MO) degradation. MO degradation pathway is proposed based on GC-MS analysis. The enhanced photoactivity can be attributed to the charge transfer and electron-hole separation from the synergistic effect of Cu₂O/TiO₂ anchored on CNF/rGH. In terms of their anti-bacterial activity towards Staphylococcus aureus and Escherichia coli, the synergistic effect of the Cu₂O/TiO₂ anchored on the CNF/rGH framework showed excellent activity towards the bacteria.

Yolk-Shelled Gold@Cuprous Oxide Nanostructures with Hot Carriers Boosting Photocatalytic Performance

Plasmonic Au nanoparticles (NPs) have been commonly used to enhance the photocatalytic activity of Cu₂O. Till now, core-shell Au NP@Cu₂O composites have been reported in previous studies. Yet, these Au@Cu₂O composites only exhibit visible light response. Other special Au nanostructures, such as Au nanorods (NRs) or Au nanobipyramids (NBPs), which possess near-infrared light absorption, were rarely used to endow the near-infrared light response for Cu₂O. In this work, for the first time, we used Au NPs, Au NRs, and Au NBPs and employed a handy and universal method to synthesize a series of yolk-shelled Au@Cu₂O composites. The results showed that the yolk-shelled Au@Cu₂O composites had much higher photocatalytic activity than their solid-shelled ones and pure Cu₂O. More importantly, yolk-shelled Au NR@Cu₂O and Au NBP@Cu₂O composites indeed presented excellent near-infrared light-driven photocatalytic activity, which were impossible for Au NP@Cu₂O and pure Cu₂O. This outstanding performance for yolk-shelled Au NR@Cu₂O and Au NBP@Cu₂O could be attributed to the transfer of abundant hot electrons from Au NRs or Au NBPs to Cu₂O, and the timely utilization of hot holes on Au through the rich pore channels on their yolk-shelled structure. Furthermore, yolk-shelled Au@Cu₂O also showed better stability than pure Cu₂O, owing to the migration of the oxidizing holes from Cu₂O to Au driven by the built-in electric field. This work may give a guide to fabricate controllable and effective photocatalysts based on plasmonic metals and semiconductors with full solar light-driven photocatalytic activities in the future.

Carbon family nanomaterials — new applications and technologies

Research on carbon-based nanomaterials (CBNMs) and their development is one of the major scientific disciplines of the last century. This is mainly because of their unique properties which can lead to improvements in industrial technology or new medical applications. Therefore, it is necessary to examine their properties such as shape, size, chemical composition, density, toxicity, etc. This article focuses on the general characteristics of nanomaterials (NMs) and their behavior when entering the environment (water and soil). In addition, it presents individual members of the graphene family including porous ecological carbon (biochar). The article mainly deals with the new potential technologies of CBNMs considering their possible toxic and genotoxic effects. This review also highlights the latest developments in the application of self-propelled micromotors for green chemistry applications. Finally, it points to the potential biomedical applications of CBNMs.

Facile fabrication of highly flexible and floatable Cu2O/rGO on Vietnamese traditional paper toward high-performance solar-light-driven photocatalytic degradation of ciprofloxacin antibiotic

In this work, we successfully demonstrated the facile fabrication of highly flexible and floatable Cu₂O/rGO on Vietnamese traditional paper (VTP) for the solar-light-driven photocatalytic degradation of the antibiotic ciprofloxacin. The catalyst membrane was prepared by the green reduction of both Cu(OH)₂ to Cu₂O nanoparticles and graphene oxide to reduced graphene oxide. VTP has a fibrous structure with tiny fibers connected like a spider web and multiple layers in the form of a multidimensional array, which functions as a flexible and highly porous supporter to the catalyst. Moreover, the microfibrillated cellulose of VTP acts as micro-capillaries to drag ciprofloxacin (CIP) close to the active sites on the Cu₂O/rGO/VTP surface, which improves the adsorption capacity and photocatalytic efficiency of ciprofloxacin. The adsorption process is best described by the pseudo-first-order and Freundlich models. The maximum photodegradation of CIP by the catalyst is more than 80% attained after 1.5 h under solar light irradiation with a fixed CIP concentration of 10 mg L⁻¹. The catalyst membrane exhibited good reusability of up to 5 cycles.

In this work, we successfully demonstrated the facile fabrication of highly flexible and floatable Cu₂O/rGO on Vietnamese traditional paper (VTP) for the solar-light-driven photocatalytic degradation of the antibiotic ciprofloxacin.

Construction of rGO wrapping Cu2O/ZnO heterostructure photocatalyst for PNP and PAM degradation

Copper and zinc composite oxides (Cu₂O/ZnO) were synthesized by an impregnation-reduction-air oxidation method. A series of Cu₂O/ZnO/rGO ternary composites were prepared by coupling with graphene oxide (GO) with different mass fractions in a solvothermal reaction system. The microscopic morphology, crystal structure, and optical characteristics of the photocatalysts were characterized. The degradation of p-Nitrophenol (PNP) and polyacrylamide (PAM) by photocatalytic materials under simulated solar irradiation were studied, and the degradation kinetics were also investigated. The results showed that cubic Cu₂O was modified by ZnO nanorods and distributed on rGO nanosheets. The ternary Cu₂O/ZnO/rGO nanocomposites have stronger simulated solar absorption ability and higher photodegradation efficiency than pure ZnO and binary Cu₂O/ZnO nanocomposites. When the amount of Cu₂O/ZnO/rGO-10 was 0.3 g L^-1, the degradation rate of 10 mg L^-1 PNP reached 98% at 90 min and 99.6% of 100 mg L^-1 PAM at 30 min. The photocatalytic degradation processes of PNP and PAM all followed the pseudo-first-order kinetic model. Free radical trapping experiments showed that superoxide radicals were the main active substances to improve photocatalytic efficiency. In addition, after four recycles, the catalytic efficiency of Cu₂O/ZnO/rGO-10 was still over 90%. It showed that Cu₂O/ZnO/rGO-10 was a promising catalyst for wastewater treatment because of its good photostability and reusability.

Sustainable Recovery of CO2 by Using Visible-Light-Responsive Crystal Cuprous Oxide/Reduced Graphene Oxide

A simple solution-chemistry method has been investigated to prepare crystal cuprous oxide (Cu2O) incorporated with reduced graphene oxide (designated as Cu2O-rGO-x, where x represents the contents of rGO = 1%, 5% and 10%) in this work. These Cu2O-rGO-x composites combine the prospective advantages of rhombic dodecahedra Cu2O together with rGO nanosheets which have been studied as visible-light-sensitive catalysts for the photocatalytic production of methanol from CO2. Among the Cu2O-rGO-x photocatalysts, the methanol yield photocatalyzed by Cu2O-rGO-5% can be observed to be 355.26 μmol g−1cat, which is ca. 36 times higher than that of pristine Cu2O nanocrystal in the 20th hour under visible light irradiation. The improved activity may be attributed to the enhanced absorption ability of visible light, the superior separation of electron–hole pairs, well-dispersed Cu2O nanocrystals and the increased photostability of Cu2O, which are evidenced by employing UV-vis diffuse reflection spectroscopy, photoluminescence, scanning electron microscopy/transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. This work demonstrates an easy and cost-effective route to prepare non-noble photocatalysts for efficient CO2 recovery in artificial photosynthesis.

Hierarchically Grown NiO-Decorated Polyaniline-Reduced Graphene Oxide Composite for Ultrafast Sunlight-Driven Photocatalysis

Polymers and transition-metal oxides have gained great interest as a photocatalyst in environmental remediation. They could be modified with each other in order to improve their activity. Here, a sunlight-responsive hierarchically structured ternary composite of nickel oxide, polyaniline, and reduced graphene oxide (NiO@PANI/RGO) has been synthesized and employed as a catalyst for dye [methylene blue (MB)] degradation. PANI/GO synthesized by interfacial polymerization acts as a matrix for the growth of NiO using a microemulsion solvothermal method, ensuing an in situ reduction of graphene oxide during the formation of a hierarchical NiO@PANI/RGO composite. Morphological studies of the as-synthesized NiO@PANI/RGO composite reveal fine NiO (10 nm) nanoparticles intercalated between the uniformly grown PANI spines (50-60 nm) over the RGO surface. The optical band gap of ∼1.9 eV calculated from the UV-vis spectrum illustrates the extended light absorption range for the NiO@PANI/RGO photocatalyst. The efficiency of 98% MB degradation within 11 min with the degradation rate constant 0.086 min-1 for NiO@PANI/RGO has surpassed any other report on metal oxide/graphene-based ternary composites. Overall, this work could pave the way for the fabrication of futuristic hierarchical structured ternary nanocomposites as an efficient photocatalyst and facilitate their application in the environmental protection issues.

Two-dimensional porous cuprous oxide nanoplatelets derived from metal-organic frameworks (MOFs) for efficient photocatalytic dye degradation under visible light

Bottom-up synthesis is a promising method to design and control the morphology of metal-organic frameworks (MOFs). Here, square shaped two-dimensional (2D) MOF nanoplatelets with a thickness of ∼80 nm and a lateral dimension of 4-6 μm were successfully synthesized through a facile solvothermal treatment of Cu(NO3)2 and 4,4'-bipyridine in the presence of polyvinyl pyrrolidone (PVP). The growth of a cross-weaved structure assembled via 1D chains linked with 4,4'-bipyridine along the layer stacking direction was hindered by PVP, resulting in a high-aspect ratio of the nanoplatelets. Subsequent annealing treatment converted the Cu-based MOFs into porous N-doped Cu2O/carbon composites, retaining the 2D square morphology. This annealed product showed a higher performance in the degradation of methyl orange under visible light compared to previously reported Cu2O composites. By using a small amount of the catalyst, the degradation rate could reach up to 2.5 mg min-1 gcat-1 as a result of the efficient absorption of visible light and high surface area of the porous catalysts.

Oxygen vacancy rich Cu2O based composite material with nitrogen doped carbon as matrix for photocatalytic H2 production and organic pollutant removal

A nitrogen doped carbon matrix supported Cu₂O composite material (Cu/Cu2O@NC) was fabricated successfully with a coordination polymer as precursor through calcination. In this composite material, Cu₂O particles with a size of about 6-10 nm were dispersed evenly in the nitrogen doped carbon matrix. After calcination, some coordinated nitrogen atoms were doped in the lattice of Cu₂O and replace oxygen atoms, thus generating a large number of oxygen vacancies. In Cu/Cu2O@NC, the existence of oxygen vacancies has been confirmed by electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS). Under visible light irradiation, Cu/Cu2O@NC exhibits excellent H₂ production with the rate of 379.6 μmol h^-1 g^-1. Its photocatalytic activity affects organic dyes, such as Rhodamine B (RhB) and methyl orange (MO). In addition to photocatalysis, Cu/Cu2O@NC also exhibits striking catalytic activity in reductive conversion of 4-nitrophenol to 4-aminophenol with in presence of sodium borohydride (NaBH₄). The conversion efficiency reaches almost 100% in 250 s with the quantity of Cu/Cu2O@NC as low as 5 mg. The outstanding H₂ production and organic pollutants removal are attributed to the oxygen vacancy. We expect that Cu/Cu2O@NC will find its way as a new resource for hydrogen energy as well as a promising material in water purification.

Fabrication of Ag-Cu2O/Reduced Graphene Oxide Nanocomposites as Surface-Enhanced Raman Scattering Substrates for in Situ Monitoring of Peroxidase-Like Catalytic Reaction and Biosensing

Highly sensitive biosensors are essential in medical diagnostics, especially for monitoring the state of an individual's disease. An ideal way to achieve this objective is to analyze human sweat secretions by noninvasive monitoring. Due to low concentrations of target analytes in human secretions, fabrication of ultrasensitive detection devices is a great challenge. In this work, Ag-Cu₂O/reduced graphene oxide (rGO) nanocomposites were prepared by a facile two-step in situ reduction procedure at room temperature. Ag-Cu₂O/rGO nanocomposites possess intrinsic peroxidase-like activity and rapidly catalyze oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. On the basis of the excellent SERS properties and high peroxidase-like activity of the Ag-Cu₂O/rGO nanocomposites, the catalytic oxidation of TMB can be monitored by SERS. This approach can detect H₂O₂ and glucose with high sensitivity and distinguish between diabetic and normal individuals using glucose levels in fingerprints. Our work provides direction for designing other SERS substrates with high catalytic activity and the potential for application in biosensing, forensic investigation, and medical diagnostics.